Does Extradition Require a Full Criminal Trial First?

Hello everyone. I have heard conflicting explanations about how extradition works in practice. Some people claim that a full criminal conviction must already exist abroad before a request can be submitted, while others say that preliminary charges are sufficient. I am trying to clarify whether a foreign government needs to complete an entire trial before seeking surrender, or whether the process can begin at an earlier investigative stage. In practical terms, what level of procedural development is typically required before U.S. courts will consider an extradition petition?